To enable cellular mobile communication networks to provide new services, such as E911 alarm, target tracking, position-based information service (e.g., searching for the optimal traffic route or the nearest petrol station), mobile station positioning technology has to be introduced to position mobile stations.
Presently, there are 3 basic methods for positioning mobile stations in cellular mobile communication networks: 1) TOA (Time Of Arrival) positioning method, which obtains distances from mobile station to corresponding bases station through measuring TOAs of a mobile station to three or more base stations and then estimates the position of the mobile station through solving a circle equation set; 2) TDOA (Time Difference Of Arrival) positioning method, which obtains distance difference to corresponding base stations through measuring TDOAs from a mobile station to three or more base stations and then estimates the position of the mobile station through solving a hyperbolic equation set; 3) a method combining CELL-ID (Cell Identifier) and TOA, which utilizes the cell identifier to determine the position of the service cell where the mobile station is in and then further determine the position of the mobile station in the cell through measuring TOA from the mobile station to the service base station.
In conventional mobile communication systems, to ensure normal communication between mobile stations and a base station, repeaters are deployed in some areas that are not covered by the base station. FIG. 1 is a structural diagram of a conventional RF repeater; in the downlink direction, the donating antenna (antenna of the service base station) picks up signals from an existing coverage area, filters off out-of-band signals with a band pass filter, and then retransmits the filtered signals to an area to be covered via a power amplifier; in uplink direction, the signals from a mobile station in the coverage area are processed similarly and then transmitted to the corresponding base station to implement signal transmission between the base station and the mobile station. The introduction of a repeater implements normal communication between mobile stations and base station in the coverage of the repeater.
However, the introduction of repeater makes mobile stations in the coverage of the repeater can't be positioned effectively. When a mobile station to be positioned is in the coverage of the repeater, TDOA positioning process will fail because the number of detected base stations is too small; even though there are enough detected base stations, what is determined finally is the position of the repeater, the position of the mobile station in the coverage of the repeater can't be determined; furthermore, the positioning system is unable to determine whether the positioning result has been affected by the repeater. Similarly, when a mobile station to be positioned is in the coverage of the repeater, due to the effect of time delay in repeater RF channel, the ‘TOA+CELL-ID’ method will result in severe TOA error, thus the mobile station can't be positioned effectively.
To ensure effective positioning of mobile stations in the coverage of the repeater, a ‘repeater+auxiliary PE (Positioning Element)’ method can be used in network deployment. However, the disadvantage of the method is: to achieve effective positioning of mobile stations, at least 3 PEs have to be deployed in the coverage of each repeater, which increases complexity of network planning as well as device procurement expense and operation and maintenance costs.